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1.
Effects of ultraviolet radiation on early larval stages of the Alpine newt, Triturus alpestris, under natural and laboratory conditions 总被引:3,自引:0,他引:3
Although Alpine newts (Triturus alpestris) are found at altitudes up to 2500 m, their larvae proved to be extremely sensitive to UV radiation when exposed in clear
tapwater to natural sunlight or to comparable artificial UV-B radiation in the laboratory. The experiments revealed severe
skin damages (lysis of epithelial cells) and mortality after a few days of exposure. In their natural habitats above the timberline,
however, the larvae are protected by the high concentration of dissolved organic carbon in the water leading to an almost
complete absorption of UV radiation within the first few centimeters of the water layer. Furthermore, when exposed to UV radiation
larvae show erratic swimming activities that may carry them into protected areas. Only in very shallow natural habitats did
we detect sublethal UV-like histological effects. Shallow high mountain ponds with clear water normally lack newt populations,
probably as a consequence of both low temperature and the effects of UV radiation.
Received: 4 October 1996 / Accepted: 7 February 1997 相似文献
2.
Non-consumptive effects of larval Salamandra on crustacean prey: can eggs detect predators? 总被引:3,自引:0,他引:3
Leon Blaustein 《Oecologia》1997,110(2):212-217
Predators affect prey populations not only by prey consumption but also in nonconsumptive ways including modifying prey behavior.
I tested the effects of fire salamander larvae (Salamandra infraimmaculata) on populations of co-occurring crustacean species in artificial outdoor pools. I also tested whether these effects were
due entirely to prey consumption by Salamandra larvae or alternatively to some nonconsumptive effect. The soil (containing crustacean eggs) added to the artificial pools
was collected from a dried-out temporary pool that is inhabited by Salamandra during the early part of the hydroperiod. I randomly assigned the pools to one of three treatments: control, free Salamandra, or caged Salamandra. Free salamander larvae could roam the entire pool and prey upon crustaceans. Caged salamander larvae were placed within
a cage with having 250-μm mesh windows. They could not prey upon the crustaceans but could, for example, influence them by
chemical cues. Densities of the three dominant crustacean species (Arctodiaptomus similis, Ceriodaphnia quadrangula and Cyzicus sp.) were drastically reduced in both salamander treatments compared to the control. Crustacean densities, however, were
not significantly different between the two salamander treatments. One plausible explanation is that crustacean eggs can detect
the presence of this predator via chemical cues and delay hatching.
Received: 4 March 1996 / Accepted, 23 October 1996 相似文献
3.
Many studies have experimentally addressed the effects of a particular predator species on prey behavior. In nature, however,
prey frequently face multiple species of predators that often vary in their predatory mode and in their level of predation
risk. Relatively few studies have considered prey responses under these complex conditions. In Kentucky, the stream-dwelling
water strider (Aquariusremigis) coexists with many potentially dangerous predators, two of which are the green sunfish (Lepomiscyanellus) and the fishing spider (Dolomedesvittatus). Green sunfish occupy stream pools and attack water striders from below. In contrast, fishing spiders hunt along stream
shorelines where they perch on overhanging vegetation or rocks and attack water striders near shore. We compared how A. remigis individuals respond to these two very different predators in pools with one or both predators. The presence of sunfish in
pools had strong effects on male water strider behavior, including increased use of three types of refuge from sunfish (riffles,
climbing out of the water, sitting on the water but at the edges of pools), decreased activity and a decreased number of aggressive
males on the water. Spiders also influenced water strider behavior; male water striders avoided spiders by shifting away from
the edges of pools. Comparisons of the effects of the two predator species showed that in general, antipredator responses
by male water striders were stronger in pools with fish alone than in those with spiders alone. In the presence of both predators,
male water strider behavior (microhabitat use and activity) was generally similar to behavior in the presence of fish alone.
In contrast, female water striders showed no significant response to the presence of sunfish, and little response to the presence
of spiders. This lack of response could be because females spent much of their time in refuges even in the absence of predators
(apparently hiding from harassment by males). Both spiders and fish caused decreases in water strider mating activity. The
presence of fish reduced both the number of matings per pool (mating frequency), and mean mating durations. Spiders induced
a decrease in mean mating duration, but not in mating frequency. The largest reductions in mating activity occurred in pools
with both predators present. Pools with either spiders or fish alone suffered 15–20% water strider mortality during our experiment
(versus no mortality in predator-free pools). Extant theory suggests that when prey face conflicting microhabitat responses
to two predators (as in this study), the predators should have facilitative effects on predation rates (i.e., prey that avoid
one predator are often killed by the other and vice versa). Mortality rates in pools with both predators present, however,
were not significantly different from that predicted by a null model of multiple predator effects. The lack of predator facilitation
can be explained by the compensatory reductions in water strider activity and mating activity in the presence of both predators.
Received: 26 August 1996 / Accepted: 12 June 1998 相似文献
4.
Fish species richness and incidence patterns in isolated and connected stream pools: effects of pool volume and spatial position 总被引:4,自引:0,他引:4
Christopher M. Taylor 《Oecologia》1997,110(4):560-566
I tested the effects of pool size and spatial position (upstream or downstream) on fish assemblage attributes in isolated
and connected pools in an upland Oklahoma stream, United States. I hypothesized that there would be fundamental differences
between assemblages in these two pool types due to the presence or absence of colonization opportunities. Analyses were carried
out at three ecological scales: (1) the species richness of pool assemblages, (2) the species composition of pool assemblages,
and (3) the responses of individual species. There were significant species-volume relationships for isolated and connected
pools. However, the relationship was weaker and there were fewer species, on average, in isolated pools. For both pool types,
species incidences were significantly nested such that species-poor pools tended to be subsets of species-rich pools, a common
pattern that ultimately results from species-specific differences in colonization ability and/or extinction susceptibility.
To examine the potential importance of these two processes in nestedness patterns in both pool types, I made the following
two assumptions: (1) probability of extinction should decline with increasing pool size, and (2) probability of immigration
should decline in an upstream direction (increasing isolation). When ordered by pool volume, only isolated pools were significantly
nested suggesting that these assemblages were extinction-driven. When ordered by spatial position, only connected pools were
significantly nested (more species downstream) suggesting that differences in species-specific dispersal abilities were important
in structuring these assemblages. At the individual-species level, volume was a significant predictor of occurrence for three
species in isolated pools. In connected pools, two species showed significant position effects, one species showed a pool
volume effect, and one species showed pool volume and position effects. These results demonstrate that pool size and position
within a watershed are important determinants of fish species assemblage structure, but their importance varies with the colonization
potential of the pools. Isolated pool assemblages are similar to the presumed relaxed faunas of montane forest fragments and
land bridge islands, but at much smaller space and time scales.
Received: 6 December 1996 / Accepted: 10 December 1996 相似文献
5.
We examined the response of the birch tube-maker Acrobasis betulella Hulst (Lepidoptera: Pyralidae) to habitat patch isolation and edges. Density of A.␣betulella larva was higher on distant islands than on islands close to the shore. Following experimental removal of all larvae from
the islands, adults were able to recolonize even the most distant islands, and larval density was again positively correlated
with the degree of isolation. Larval density was not correlated with island size or the amount of birch present on the islands.
Larvae on more distant islands did not have lower mortality than those in less isolated sites. Larvae were found more often
on edges than in the interior of birch stands and developed faster on edges. This positive edge effect, coupled with the ability
of the adults to disperse to even our most distant islands, suggests that A. betulella would be favored in an environment fragmented at the same scale as our island system.
Received: 15 April 1996 / Accepted: 30 September 1996 相似文献
6.
Effects of changes in atmospheric carbon dioxide on the location of hosts by the moth, Cactoblastis cactorum 总被引:3,自引:0,他引:3
Gert Stange 《Oecologia》1997,110(4):539-545
Sensory organs that detect CO2 are common in herbivorous moths and butterflies, but their function has been unclear until now. As the CO2 gradients in the vicinity of a host plant depend on its physiological condition, CO2 could provide a sensory cue for the suitability of the plant as a larval food source. This study investigated whether changing
the atmospheric CO2 concentration affected oviposition by Cactoblastis cactorum on its host, the cactus Opuntia stricta. On host plants exposed to rapid fluctuations in CO2 concentration, the frequency of oviposition was reduced by a factor of 3.2 compared to the control. As the fluctuations mask
the much smaller CO2 signals generated by the plants, this suggests that those signals constitute an important component of the host identification
process. On host plants exposed to a constant background of doubled CO2, oviposition was also reduced, by a factor of 1.8. An increased background reduces host signal detectability, partially as
a consequence of a general principle of sensory physiology (Weber-Fechner's law), and partially due to other factors specific
to CO2-receptor neurons.
Received: 4 October 1996 / Accepted: 16 January 1997 相似文献
7.
G. Maenhaut-Michel R. Janel-Bintz N. Samuel R. P. P. Fuchs 《Molecular & general genetics : MGG》1997,253(5):634-641
The potency of 2-amino-3-methylimidazo(4, 5-f)quinoline (IQ) adducts to induce −2, −1 and +1 frameshift mutations has been determined on specific target DNA sequences,
namely short runs of alternating GpC sequences and short runs of guanines. The genetic control of the mutational processes
has been analyzed using different Escherichia coli mutants, affected either in the control or in the mutagenesis pathway of the SOS system. We have shown that IQ adducts induce
very efficiently both −1 and −2 frameshift mutations in E. coli. Both types of deletion mutations are induced in bacteria without the need of SOS induction, indicating that no LexA-controlled
functions, in particular the UmuDC proteins, are required for mutation fixation. We have also shown that the frequency of
IQ-induced −2 frameshift mutations in alternating GC sequences increases with the length of the repetition. The efficiency
of IQ adducts to induce −1 and −2 frameshift mutations is similar to that of N‐2-acetylaminofluorene (AAF) adducts. Both chemicals are potent carcinogens which form covalent adducts at the C8 position
of guanines. We suggest that in both cases the adduct-induced DNA structure allows the replication complex to perform a mutagenic
bypass of the lesion by a slippage mechanism. However, in contrast to AAF-induced frameshift mutagenesis, IQ-induced frameshift
mutagenesis is SOS-independent.
Received: 13 June 1996 / Accepted: 24 September 1996 相似文献
8.
Background matching might lower the risk of seeds being eaten by seed predators that search visually. In aviary experiments,
we analyzed the selection of diff erent-colored seeds by ground-feeding finches (Fringillacoelebs and F.montifringilla) against four naturally occurring forest soil substrates. The substrates were fresh burn (black), 6-year-old burn (brown),
mineral soil (pale yellow) and Pleuroziumschreberi feather moss (green). We used color-sorted seeds of Pinussylvestris, a species with a large natural variation in seed color, ranging from pale yellow to black. Although seeds were scattered
on the substrates at a density of only 91 seeds m−2, birds removed seeds effectively. Both bird species found more pale than dark seeds on the fresh burn substrate. F. montifringilla also recovered more pale than dark seeds on the old burn, and more dark than pale seeds on mineral soil. In moss, the birds
found very few seeds compared to the other substrates, and there was no color discrimination. P.sylvestris is frequently regenerating after fire, suggesting that dark seeds would be favored under selection from visually searching
predators. Fire-adapted conifers with serotinous cones, e.g., Pinuscontorta ssp. latifolia, which spread their seeds primarily on freshly burnt surfaces, produce uniformly black or dark brown seeds. However, regeneration
of the non-serotinous P.sylvestris is often extended for several years after a fire, during which substrate color and structure change. This may have helped
to maintain variation in seed color. When regeneration of a plant species occurs on a substrate of uniform color, we believe
that selection by visually searching seed predators will result in the evolution of cryptic seed color.
Received: 16 August 1996 / Accepted: 30 November 1996 相似文献
9.
S. B. Chaplin M. M. Munson S. T. Knuth 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(3):197-203
The effect of various activity regimes on metabolism of pigeon pectoralis was examined by measurement of blood lactate following
exercise, total lactate dehydrogenase activity of pectoral muscle, and proportions of specific isoenzymes of pectoral muscle
lactate dehydrogenase. Sprint-trained birds had the highest pectoral muscle lactate dehydrogenase activity (1409 IU · g−1 wet tissue), while endurance-trained birds had the highest peak lactate levels (287 mg · dl−1, extrapolated from decay curves) and fastest half-time of the lactate response (4.8 min) following exercise, but the lowest
lactate dehydrogenase activity (115 IU · g−1 wet tissue). Immobilization of one wing for 3 weeks following endurance training produced a marked increase in lactate dehydrogenase
activity of the immobilized muscle, compared to that in the contralateral pectoralis and endurance-trained muscle. Aerobic
forms of the lactate dehydrogenase enzyme (that favor conversion of lactate to pyruvate) predominated in pectoral muscle of
endurance-trained birds, while cage-confined birds exhibited primarily the anaerobic isoenzymes. These results demonstrate
that conversion of pectoral muscle lactate dehydrogenase isoenzymes, total lactate dehydrogenase activity, and half-time of
lactate response after exercise is dependent on activity regime in pigeons. In this respect, pigeon pectoral muscle responds
to training and disuse in a manner similar to that of mammalian skeletal muscle.
Accepted: 10 September 1996 相似文献
10.
Light response characteristics of a morphologically diverse group of southern hemisphere conifers as measured by chlorophyll fluorescence 总被引:5,自引:0,他引:5
Unlike northern hemisphere conifer families, the southern family, Podocarpaceae, produces a great variety of foliage forms
ranging from functionally broad-, to needle-leaved. The production of broad photosynthetic surfaces in podocarps has been
linked qualitatively to low-light-environments, and we undertook to assess the validity of this assumption by measuring the
light response of a morphologically diverse group of podocarps. The light response, as apparent photochemical electron transport
rate (ETR), was measured by modulated fluorescence in ten species of this family and six associated species (including five
Cupressaceae and one functionally needle-leaved angiosperm) all grown under identical glasshouse conditions. In all species,
ETR was found to increase as light intensity increased, reaching a peak value (ETRmax) at saturating quantum flux (PPFDsat), and decreasing thereafter. ETRmax ranged from 217 μmol electrons · m−2 · s−1 at a PPFDsat of 1725 μmol photons · m−2 · s−1 in Actinostrobus acuminatus to an ETR of 60 μmol electrons · m−2 · s−1 at a PPFDsat of 745 μmol electrons · m−2 · s−1 in Podocarpus dispermis. Good correlations were observed between ETRmax and both PPFDsat and maximum assimilation rate measured by gas-exchange analysis. The effective quantum yield at light saturation remained
constant in all species with an average value of 0.278 ± 0.0035 determined for all 16 species. Differences in the shapes of
light response curves were related to differences in the response of non-photochemical quenching (q
n), with q
n saturating faster in species with low PPFDsat. Amongst the species of Podocarpaceae, the log of average shoot width was well correlated with PPFDsat, wider leaves saturating at lower light intensities. This suggests that broadly flattened shoots in the Podocarpaceae are
an adaptation to low light intensity.
Received: 15 April 1996 / Accepted: 30 September 1996 相似文献
11.
Alternative fire resistance strategies in savanna trees 总被引:9,自引:0,他引:9
Bark properties (mainly thickness) are usually presented as the main explanation for tree survival in intense fires. Savanna
fires are mild, frequent, and supposed to affect tree recruitment rather than adult survival: trunk profile and growth rate
of young trees between two successive fires can also affect survival. These factors and fire severity were measured on a sample
of 20 trees near the recruitment stage of two savanna species chosen for their contrasted fire resistance strategies (Crossopteryx febrifuga and Piliostigma thonningii). Crossopteryx has a higher intrinsic resistance to fire (bark properties) than Piliostigma: a 20-mm-diameter stem of Crossopteryx survives exposure to 650°C, while Piliostigma needs a diameter of at least 40 mm to survive. Crossopteryx has a thicker trunk than Piliostigma: for two trees of the same height, the basal diameter of Crossopteryx will be 1.6 times greater. Piliostigma grows 2.26 times faster than Crossopteryx between two successive fires. The two species have different fire resistance strategies: one relies on resistance of aboveground
structures to fire, while the other relies on its ability to quickly re-build aboveground structures. Crossopteryx is able to recruit in almost any fire conditions while Piliostigma needs locally or temporarily milder fire conditions. In savannas, fire resistance is a complex property which cannot be assessed
simply by measuring only one of its components, such as bark thickness. Bark properties, trunk profile and growth rate define
strategies of fire resistance. Fire resistance may interact with competition: we suggest that differences in fire resistance
strategies have important effects on the structure and dynamics of savanna ecosystems.
Received: 16 August 1996 / Accepted: 4 January 1997 相似文献
12.
Blair M. Goodridge Erin J. Hanan Rosana Aguilera Erin B. Wetherley Ying-Jung Chen Carla M. D’Antonio John M. Melack 《Ecosystems》2018,21(8):1608-1622
Wildfires alter nitrogen (N) cycling in Mediterranean-type ecosystems, resetting plant and soil microbial growth, combusting plant biomass to ash, and enhancing N availability in the upper soil layer. This ash and soil N pool (that is, wildfire N) is susceptible to loss from watersheds via runoff and leaching during post-fire rains. Plant and soil microbial recovery may mitigate these losses by sequestering N compounds in new biomass, thereby promoting landscape N retention in N-limited chaparral ecosystems. We investigated the relative balance between wildfire N loss, and plant and soil microbial N uptake and stream N export for an upland chaparral watershed in southern California that burned (61%) in a high-intensity wildfire in 2009 by using a combination of stream, vegetation, soil microbial, and remote sensing analyses. Soil N in the burn scar was 440% higher than unburned soil N in the beginning of the first post-fire wet season and returned within 66 days to pre-fire levels. Stream N export was 1480% higher than pre-fire export during the first post-fire rain and returned within 106 days over the course of the following three rainstorms to pre-fire levels. A watershed-scale N mass balance revealed that 52% of wildfire N could be accounted for in plant and soil microbial growth, whereas 1% could be accounted for in stream export of dissolved nitrogen. 相似文献
13.
We studied the possible role of resource limitation and interspecific competition in assemblages of dabbling ducks on breeding
lakes in Finland and Sweden with observational and experimental data. After initial vegetation mapping and yearly censuses
of ducks in 1985–1990, we collected observational data in 1991–1994 from 28 lakes with natural populations of mallard Anas platyrhynchos and teal A. crecca. Mallard and teal co-occur over vast areas in the Holarctic and they are the only breeding dabbling ducks on many oligotrophic
lakes. Both species are migratory in our study regions, teal arriving later in spring than mallards. Log-linear model analysis
of observational presence/absence data revealed a positive, not a negative, association between the species. This association
was independent of habitat diversity as well as of lake size. Mallard-teal interaction was also studied in a cross-over introduction
experiment in 32 other lakes in two years. Wing-clipped mallards were introduced to breeding lakes before the arrival of teal
to induce resource limitation and interspecific competition, hypothesized to reduce lake use by teal. The density of mallard
pairs on experimental lakes was 2.9–8.0 times higher than on controls, but there was no negative response by teal to the treatment.
This is the first combined observational-experimental demonstration of lack of interspecific competition in waterfowl. Our
results indicate that heterospecific attraction may affect species co-existence in dabbling ducks.
Received: 28 October 1996 / Accepted: 13 January 1997 相似文献
14.
Evidence for NO-dependent vasodilation in the trout (Oncorhynchus mykiss ) coronary system 总被引:1,自引:0,他引:1
T. Mustafa C. Agnisola J. K. Hansen 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(2):98-104
The effects of l-arginine, and its analogues N
ω-nitro-l-arginine methyl ester and N
ω-nitro-l-arginine on vascular resistance were investigated in the intact coronary system of an isolated non-working trout heart preparation.
l-Arginine, at 10–8 mol · l–1induced a slight vasodilatory effect (max 10%). N
ω-nitro-l-arginine methyl ester and N
ω-Nitro-l-arginine in the range 10–8–10–4 mol · l–1 caused dose-dependent increases in coronary resistance. The vasodilatory action of l-arginine was abolished when the preparation was pretreated with 10–4 mol · l–1
N
ω-nitro-l-arginine or N
ω-nitro-l-arginine methyl ester. Nitroprusside alone at 1 mmol · l–1 induced a maximum vasodilation (30%) of the coronary system. Methylene blue a known inhibitor of guanylate cyclase, induced
a strong vasoconstriction (already significant at 10–5 mol · l–1) and was able to overcome the vasodilative effect of nitroprusside. The endothelial nitric oxide agonists acetylcholine and
serotonin, established in mammalian vessels, also mediate vasodilation in trout coronary system. In 50% of preparations, acetylcholine
induced a biphasic response with vasodilation at low concentration (max 15% at 10–8 mol · l–1). Serotonin displayed a dose-response vasodilation in the range 10–8–10–4 mol · l–1 (max 20%). These vasodilative effects were reduced or abolished by 10–4 mol · l–1
l-NA. These data support the existence of NO-mediated vasodilation mechanisms in the trout coronary system.
Accepted: 1 July 1996 相似文献
15.
Todd E. Minchinton 《Oecologia》1997,111(1):45-52
Variation in the recruitment of benthic marine invertebrates is often attributed to the interaction of the supply of new
individuals to a habitat and the availability of space for colonisation when they arrive. Also important in determining variation
in recruitment is the response of the larvae to the characteristics of the habitat. Larvae of many benthic marine invertebrates
have shown great specificity of requirements in setting their limits of distribution at the time of selection of a habitat.
The tubeworm Galeolaria caespitosa shows great variation in recruitment from place to place on rocky intertidal seashores and is a gregarious animal with larvae
showing directed responses to conspecific adults on the substratum. I hypothesised that, if variation in recruitment of G. caespitosa were independent of conditions on the substratum, the magnitude of recruitment in patches of the same shape but different
sizes cleared within continuous mats of conspecific adults would be directly related to the area available for colonisation
in the patch. Alternatively, if variation in recruitment were due to the response of larvae to conspecific adults on the substratum,
the magnitude of recruitment would be a function of the perimeter of the patch, which, given patches of the same shape, is
a measure of the influence of conspecific adults in that patch. To distinguish between these alternatives, small (area = 25 cm2; perimeter = 20 cm) and large (area = 225 cm2; perimeter = 60 cm) square patches were cleared within continuous mats of conspecific adults at four sites and recruitment
of G. caespitosa was monitored over two seasons of recruitment. The density of recruits per unit area was, on average, almost three times
greater in small than in large patches, indicating that recruitment of G. caespitosa is not directly related to the area of the patch. In contrast, the density of recruits per unit perimeter was not significantly
different between small and large patches, indicating that recruitment of G. caespitosa is related to the proximity of conspecific adults in the patch. Therefore, at a given site, the perimeter of patches within
mats of G. caespitosa is a better predictor of the relative magnitude of recruitment among patches than that provided by their areas. These results
are contrary to many models of invertebrate recruitment that assume close linkage between available space on the substratum
and settlement. Moreover, they highlight the importance of behavioural responses of animals at the time of selection of habitat
in accounting for variation in recruitment. For populations of organisms that display gregarious behaviour at settlement,
or conspecific attraction, this direct relationship between the perimeter of patches and recruitment could be used as a tool
in restoring populations to disturbed habitats. The added benefit of such facilitative interactions in restoring populations
is that they provide increasing returns to the population for a given supply of potential colonists to a habitat.
Received: 1 November 1996 / Accepted: 20 January 1997 相似文献
16.
In this study we used pinfish (Lagodon rhomboides) in field experiments to examine linkages between intertidal saltmarsh and adjacent subtidal habitats. Pinfish are more
than twice as abundant in intertidal marshes adjacent to seagrass beds than in those adjacent to the unvegetated subtidal
bottom. Movement of pinfish between the marsh edge and the adjacent subtidal habitat was greater for fish captured in areas
with both intertidal and subtidal vegetation than in those with intertidal vegetation and adjacent unvegetated mudflats. This
movement provides an important link between habitats, allowing transfer of marsh-derived secondary production to subtidal
seagrass beds and vice versa. Pinfish held in enclosures with both intertidal and subtidal vegetation were, on average, approximately
90% heavier than fish held in enclosures with intertidal vegetation and unvegetated subtidal bottom. Because saltmarshes and
seagrass beds contribute to the production of living marine resources, active measures are being taken to preserve and restore
these habitats. The results from this study have direct application to decisions concerning site selection and optimal spatial
proximity of saltmarsh and seagrass habitats in the planning of restoration and mitigation projects. To maximize secondary
production and utilization of intertidal marshes, managers may opt to restore and/or preserve marshes adjacent to subtidal
seagrass beds.
Received: 31 May 1996 / Accepted: 23 October 1996 相似文献
17.
Bernd Schröder Ina Rittmann Ernst Pfeffer Gerhard Breves 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(1):43-51
Unidirectional flux rates of Ca2+ across gastrointestinal tissues from sheep and goats were measured in vitro by applying the Ussing-chamber technique. Except for the sheep duodenum, mucosal to serosal Ca2+ flux rates (J
ms) exceeded respective flux rates in the opposite direction (J
sm) in both species and in all segments of the intestinal tract. This resulted in net Ca2+ flux rates␣(J
net = J
ms − J
sm) ranging between −2 and 9 nmol · cm−2 · h−1 in sheep and between 10 and 15 nmol cm−2 · h−1 in goats. In sheep, only J
net in jejunum, and in goats, J
netin duodenum and jejunum were significantly different from zero. Using sheep rumen wall epithelia, significant J
net of Ca2+ of around 5 nmol · cm−2 · h−1 could be detected. Since the experiments were carried out in the absence of an electrochemical gradient, significant net
Ca2+ absorption clearly indicates the presence of active mechanisms for Ca2+ transport. Dietary Ca depletion caused increased calcitriol plasma concentrations and induced significant stimulations of
net Ca2+ absorption in goat rumen. J
net of Ca2+ across goat rumen epithelia was significantly reduced by 1 mmol · l −1 verapamil in the mucosal buffer solution. In conclusion, there is clear evidence for the rumen as a main site for active
Ca2+ absorption in small ruminants. Stimulation of active Ca2+ absorption by increased plasma calcitriol levels and inhibition by mucosal verapamil suggest mechanistic and regulatory similarities
to active Ca2+ transport as described for the upper small intestines of monogastric species.
Accepted: 31 July 1996 相似文献
18.
A. D. Blest Sally Stowe 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1997,180(4):347-355
(1) In vitro retinas of a crab, Leptograpsus, were treated with a phospholipase inhibitor, manoalide, or a G-protein activator, Mas-7. Both drugs address early stages
of the phototransduction cascade. (2) Manoalide inhibited the light-dependent reduction of rhabdoms during the `day' phase
of the light cycle, but did not induce rhabdom overgrowth. Following a period of darkness manoalide failed to affect the diminution
of illuminated rhabdoms. (3) The diminution of rhabdoms that follows photoreceptor depolarisation induced by 100 mmol · l−1 K+ in darkness was not affected by 2␣μmol · l−1 manoalide. (4) When retinas in the `night' phase were treated with Mas-7 in darkness, rhabdom diameters were augmented, concurrently
with endocytosis of photoreceptor plasma membranes. (5) The results of combining manoalide and Mas-7 with actinomycin D, U-57908
or okadaic acid, drugs used in previous studies to manipulate steps notionally lower in the transduction cascade, lead to
a hypothetical model for the regulation of phototransductive membrane turnover by arthropods.
Accepted: 3 October 1996 相似文献
19.
Ralph Beneke Katharina Meyer 《European journal of applied physiology and occupational physiology》1997,75(3):246-251
The effect of a 3-week exercise programme on performance and economy of walking was analysed in 16 male patients with chronic
heart failure [mean age 51.8 (SD 6.9) years, height 174.9 (SD 6.3) cm, body mass 75.3 (SD 11.5) kg, ejection fraction 20.8
(SD 5.0)%]. They were submitted to a cardiopulmonary exercise test on a cycle ergometer and a 6-min walking test on a treadmill
before and after the period of exercise training. The training programme consisted of interval cycle (five times a week for
15 min), and treadmill ergometer training (three times a week for 10 min) at approximately 70% cycling peak oxygen uptake
(O2peak) and supplementary exercises (three times a week for 20 min). Compared to the pre values cycling O2peak [11.9 (SD 2.9) vs 14.0 (SD 2.3) ml · kg–1 · min–1], maximal self paced walking speed [0.68 (SD 0.33) vs 1.16 (SD 0.30) m · s–1], and net walking power [2.16 (SD 0.89) vs 2.73 (SD 0.91) W · kg–1] had increased (P < 0.01) while net energy cost [3.31 (SD 0.66) vs 2.33 (SD 0.38) J · kg–1 · m–1] had decreased (P < 0.001) after the training period. Approximately 42% of the increase of walking speed resulted from a higher walking power
output, whereas approximately 58% corresponded to a positive effect on walking economy. The improvement in walking economy
was a function of an increase in walking velocity itself and a result of a more efficient walking technique. These results
would indicate that in patients with marked exercise intolerance, adequate exercise training programmes could contribute to
favourable metabolic changes with positive effects on the economy of motion.
Accepted: 29 August 1996 相似文献
20.
Stephen F. Matter 《Oecologia》1997,110(4):533-538
The relationship between population density and the size of host plant patches was investigated for the red milkweed beetle
Tetraopestetraophthalmus inhabiting unmanipulated patches of Asclepias syriaca. The resource concentration hypothesis proposes that density-area patterns, specifically that of increasing herbivore density
with patch size, are primarily a function of movement between host plant patches. This research investigated the degree to
which movement accounted for density-area patterns. Poisson regression analysis of beetle abundance versus milkweed patch
size revealed that beetle density tended to increase with patch size. The pattern of density and patch size resulted from
local reproduction and residence time. The density of emerging beetles tended to increase with patch size while emigration
rates were unrelated to patch size. Immigration rates were constant with patch size for male beetles, and decreased with patch
size for female beetles. Net flux of beetles (immigration – emigration) did not vary with patch size for male beetles and
decreased with patch size for female beetles. Comparisons are made between this system and previously studied systems where
movement plays a significant role in forming density area patterns. Additionally, several hypotheses are presented which may
account for greater in situ recruitment and residence time in large patches.
Received: 23 February 1996 / Accepted: 8 January 1997 相似文献